For the coating of paper or cardboard webs with viscous coating materials or coating materials which are applied by doctoring or jet coating, especially pigmented materials, sizings and the like, it is important to provide the coating apparatus with the ability to control the cross section of the coating applied, i.e. the transverse profile, both in terms of the basis weight (weight per unit area of the coating) or the thickness thereof. For that purpose a row of adjusting elements may be provided across the width of the web which can control the local basis weight or thickness so that the result of effective positioning of these elements individually is control of the transverse profile. Usually the goal is to eliminate variations in the transverse profile which may result in the production of the coated web and the goal is to insure a uniform coating.
In the coating of paper or cardboard webs, so-called doctor blade apparatuses may be provided in which an excess of the coating material, for example a coloring matter, in a viscous form is applied and the excess is doctored off by an elastic doctoring blade which can also be referred to as a shaving or scraping blade and which removes that excess, leaving a uniform coating. The level of the basis weight of the coating remaining on the web can be adjusted by locally varying the pressing force of the blade against the coating on the web. The blade can thus be backed by a bendable bar upon which the setting elements act.
Such a doctor blade arrangement is described in WO 93/17795 and here the flexible bar is provided with a row of setting elements for adjusting locally varying pressing forces. Each setting element comprises an axially-shiftable rod or pin guided in a holder and positionable by a set screw against the force of a compression spring. The compression spring, the screw and the rod act axially.
In DE-OS 44 32 177, a so-called free jet nozzle applicator is disclosed which utilizes a slit nozzle formed between two lips from which a free jet of the coating material is directed against the web or an applicator roller which applies film of coating material formed on that roller to the web. To adjust a certain transverse profile of the coating of the two lips of the slit nozzle may be yieldable and can be adjusted differently in different zones over its length relative to the other lip. The adjusting elements are adjusting screws spaced apart across the width of the web, prestressed by spring elements. The actuation of the adjusting screws is effected either manually or by means of servomotors or the like.